Just past 10 p.m. in Cairo, around 1,500 protesters gathered outside the walls of the heavily fortified U.S. embassy in Cairo, lustily shouting anti-American slogans and promising, as one chant went, to “bring America to the ground.” The sheer rage on display was somewhat curious, since half the protesters seemed to be busy explaining to the other half just what they were all so upset about. “So this was a film on that Youtube, right,” one older protester asked a younger one. “What’s in it?”

The younger man replied, “I saw it and I can’t even repeat to you what’s in it. It’s so horrible.”

The term “storming” — deployed in initial breathless media reports — is probably a little strong for what took place in Cairo. But in Benghazi, Libya‘s second city, Salafist extremists did indeed raid the U.S. consulate, attacking with heavy weaponry, including RPGs, and killing at least one American staffer and wounding others. According to the BBC, the building burned to the ground. The U.S. has issued a strong condemnation of the incident.

In Cairo, protesters scaled the wall surrounding the citadel-like embassy that sits just off of Tahrir Square in Cairo’s posh Garden City district. They made no move to enter or damage embassy buildings, but they did remove the American flag from a pole that stood just inside the embassy walls and replaced it with a black flag bearing the slogan “there is no God but God and Muhammad is his messenger.” That’s often described as the flag of Al Qaeda, but is really more of an all-purpose banner for militant Islamists of all stripes.

The spark that provoked this sudden spasm of rage appears to be a virtually unknown anti-Islamic video allegedly promoted by notorious Muslim-baiting American preacher Terry Jones. According to the Wall Street Journal and the Associated Press, the film was produced by a 52-year-old Israeli-American Islamophobe in Southern California named Sam Bacile. The Atlantic published a useful explainer on the film in question, along with several clips. One trailer shows a bearded, frenzied Muslim mob attacking an upstanding Christian doctor and his family. The film also depicts the Prophet Muhammad as a dimwitted and lecherous “bastard” and includes a borderline pornographic depiction of Muhammad’s courtship with his first wife Khadija. It is, to put it bluntly, deeply nasty and hopelessly amateur—resembling the class project of a particularly bigoted set of Sunday school students.

Nevertheless, this video has gradually built momentum in Egypt, with an array of televised sheiks decrying it and vastly overstating its reach and importance. On this clip (in Arabic) an unidentified Muslim clergyman recounts the gory details of the video and alleges that the full film is set to be “broadcast on September 11.” The sheik goes on to rail against prominent Egyptian Christian activists abroad, implying that they were involved in the film’s production. “Since 2010, [Muslims] have been denigrated and attacked and nobody speaks up,” he concludes.

Of course, with the chaos that followed the 2005 publishing of crass, supposedly satirical cartoons of the Prophet Muhammad in a right-wing Danish newspaper, the world has seen such hostile Muslim reactions before. Islamic doctrine, even among moderate and mainstream Muslims, absolutely forbids any visual depiction of Prophet Muhammad—even respectful ones. That opposition to idolatry is one of the historical reasons Muslim artists excelled in less directly representational art forms like calligraphy or the elaborately patterned designs that adorn mosques and old palaces alike.

But the protesters also seemed genuinely unaware just how small a fringe pulpit extremists like Jones control; some seemed to be under the impression that the video was being widely broadcast on multiple American television channels —when in truth most Americans probably never heard of this video until the embassy was attacked. This was essentially a case of an American group of fringe Christian fundamentalists successfully provoking and enraging a similar group of fringe Muslim fundamentalists. The U.S. embassy in Cairo issued a statement condemning attacks on all religions; on Twitter, it said the attacks would not dissuade it “from defending freedom of speech AND criticizing bigotry.”

As of 11 p.m. in Cairo, a tense but stable standoff was in place outside the embassy. An extremely angry, mostly Islamist crowd of protesters remained gathered outside the walls. The flagpole in question was bare, but half a dozen protesters remained perched on top of the walls waving Islamic flags. A hopelessly insufficient contingent of Egyptian riot police were deployed in front of the wall—which was now covered in bilingual graffiti decrying the U.S. and citing Koranic verse. The riot police were making no move to disperse the protesters and the protesters seemed to be making no moves to re-enter the embassy grounds.

Exactly how a group of unarmed radicals even managed to make it a few feet onto the ground of the heavily guarded embassy remains a mystery. It’s safe to assume that the contingent of marines who guard the embassy around the clock made a decision that shooting Egyptian civilians on Sept. 11 was inadvisable. But the normally robust Egyptian security forces seemed to take an unusually soft approach.

The long-term ripples from Tuesday’s incident should be significant. For starters, the implication that Egyptian Coptic Christians in the U.S. were involved, like Jones, in promoting the video can only damage tenuous relations with Egypt’s already nervous 10% Coptic minority.

It’s unlikely that this will provoke any sort of serious crisis between Washington and President Mohamed Morsy’s young administration. But the image of Egyptians tearing down the American flag instantly damns Morsy’s efforts to project an atmosphere of stability and post-revolution order. In a moment of depressing irony, the news of the embassy incident broke during the closing press conference of a U.S.-sponsored trade delegation in Egypt—with American CEOs hailing Egypt as a prime spot for foreign investment.

Ashraf Khalil is a Cairo-based journalist and author of Liberation Square: Inside the Egyptian Revolution and the Rebirth of a Nation.